The present invention relates to fuel lance apparatus and methods for spraying liquid and/or gaseous fuels into a combustion chamber, particularly as used in gas turbines.
Publication DE-A1-43 26 802 discloses a fuel lance which is at present used by the applicant in his gas turbines (in this respect see also publications U.S.Pat. No. 5,431,018, U.S. Pat. No. 5,626,017 and EP-A1-0 620 362). In this case, the nozzles for gaseous fuel and liquid fuel (oil, etc.) are combined.
The development of the oil spraying of the primary burners (EV burners) led to the plain-jet principle. In this case, the liquid fuel is sprayed as a jet through a central bore into the burner. The fuel jet disintegrates in the swirl zone of the EV burner (in this respect see, for example, EP-B1-0 321 809). Depending on the adaptation of the impulse ratio between the liquid-fuel jet and the surrounding air flow, the location of the jet disintegration can be set.
The known radial spraying of the liquid fuel of the SEV chamber and the atomizing of the liquid fuel by means of an air-blast nozzle leads to a relatively large quantity of water having to be admixed with the liquid-fuel spray jet in order to prevent a flame flashback.
The object of the invention is therefore to provide a fuel lance for the spraying of liquid fuel and/or gaseous fuel in a secondary or tertiary burner, which fuel lance avoids the above-described disadvantages of previous lances and permits in particular a reduction in the retention time of the liquid fuel in the premix section and thus a reduction in the admixed proportion of water.
The essence of the invention consists in spraying the liquid fuel axially in the main flow direction by means of a plain-jet nozzle. The result of this type of spraying is that the retention time of the liquid fuel in the premix section is reduced and thus less water has to be added in order to prevent a flame flashback.
A first preferred embodiment of the fuel lance according to the invention is comprises a central liquid-fuel tube, which is arranged concentrically to a lance axis and encloses the liquid-fuel passage for directing a liquid fuel, and a gas tube, which encloses the liquid-fuel tube and forms between it and the liquid-fuel tube a gas passage for directing a gaseous fuel, and a lance shell, which encloses the gas tube and forms between it and the gas tube an air passage for directing cooling or atomizing air, and also second means for spraying the gaseous fuel from the gas passage into the combustion chamber, and third means for spraying the air from the air passage into the combustion chamber, the lance axis being oriented essentially parallel to the main flow direction. This permits a flexible mode of operation with different fuels or fuel combinations in a compact construction.
The axial liquid-fuel jet of the fuel lance according to the invention is preferably surrounded by an air veil. This is achieved in a second embodiment of the invention in that the liquid-fuel nozzle is arranged centrally in the lance axis, and in that the third means comprise first nozzle means which are designed in such a way that the liquid-fuel jet discharging axially through the liquid-fuel nozzle is surrounded in a sheath-like manner by a likewise axially discharging air veil, either the first nozzle means comprising a plurality of axially oriented bores which are arranged in a distributed manner around the liquid-fuel nozzle, or the first nozzle means comprising an annular gap which concentrically surrounds the liquid-fuel nozzle.
The air for the air veil around the liquid-fuel jet is preferably utilized at least for the partial cooling of the lance head. This is done in a development of the second embodiment of the invention by the first nozzle means or bores or the annular gap being connected to the air passage via a head passage, running through the lance head, in such a way that the lance head is cooled by the air flowing in the head passage.
In a further preferred embodiment of the invention, the gaseous fuel from the gas passage is sprayed radially into the combustion chamber through individual nozzle openings oriented radially to the lance axis, the gas jet from the nozzle openings in each case being surrounded concentrically by an air sheath, and the nozzle openings for the gaseous fuel in each case being formed by a radially arranged guide tube, which is connected to the gas passage and opens into the combustion chamber through a shell opening in the lance shell, and the shell opening, relative to the outside diameter of the guide tube, being selected in such a way that an annular gap remains free for producing the air sheath surrounding the gas jet.
A lance according to another preferred embodiment has an especially simple geometry. The gaseous fuel is sprayed concentrically to the liquid fuel as a plain jet essentially parallel to the main flow direction. The two fuel jets are concentrically surrounded by an air sheath. A first annular gap, which concentrically surrounds the liquid-fuel nozzle, is provided for spraying the gaseous fuel. A second annular gap, which concentrically surrounds the first annular gap, is provided for forming the air sheath.
The method according to the invention for operating such a fuel lance is characterized in that in each case liquid fuel is sprayed into the combustion chamber through the liquid-fuel nozzle and air is sprayed into the combustion chamber through each of the first and second annular gaps.
Furthermore, it is conceivable for the axial part, formed parallel to the main flow direction, of the fuel lance to be shortened if the inflowing swirl zone (of the hot gases) is configured in such a way that no wake zone occurs. An embodiment of the lance in which the liquid fuel is sprayed directly at the radial holder or supporting arm is therefore also conceivable (4 in FIG. 1 of DE-A1-43 26 802). This stem may be designed to be profiled in a more or less fluidically favorable manner. According to the invention, the preferred spraying is effected axially via a plain jet, and accordingly perpendicularly to the main flow direction for the air-sheathed gaseous fuel. This embodiment has the advantage that the lance is easier to fit and requires less cooling air.